Coated sheet material



Patented Jan. 18, 1944 COATED SHEET MATERIAL Allen Abrams and George W. l 'orcey, Wausau,

and Charley L. Wagner, Menasha, Wis,

signors to Marathon Paper ,Mills Company, Rothschild, Wis., a corporation of Wisconsin No Drawing. Application August 2, 1940,

Serial No. 349,767

Claims.

This invention relates to a coated sheet material, having a thermoplastic composition, suitable for the packaging of food products and the like.

An object of the invention is to provide a coated sheet material having a continuous thermoplastic flexible film thereon suitable for packaging of molten food materials such a process cheese, chocolate, candy, jellies and the like, and which coated sheet will remain flexible and pliable upon cooling of the goods packaged therewith.

A further object of the invention is to provide a coated sheet material having a flexible, continuous, thermoplastic coating film thereon suitable for packaging foods and adapted to be in contact with hot or molten foods and which will retain the self-sustaining characteristics as well as flexibility of the film after cooling of the food and will not become brittle, but will adhere to the sheet material in a continuous fllm.

Still another object of the invention is to provide a sheet material coated with a wax-rubber coating composition so compounded as to provide a continuous flexible film adapted for packaging foods in molten condition, and which will and 2,054,113. disclose a composition comprising wax and rubber suitable for coating sheet materials. The sheet materials are coated with a hot-melt wax-rubber composition having a viscosity of at least 8,000 seconds (50 cc. measured on a Scott viscosimeter at 90 C.) We have found that when the coated sheet materials made according to these patents are used for packaging hot or molten food products, particularly when such food products are brought into direct contact with the coating composition or film on the sheet material, there is a tendency for the coating on the sheet to soften, and upon cooling the coating film loses its original flexibility and does not retain its original self-sustaining characteristics. 0n cooling the coating also tends to become brittle, so that when the package is opened, the coating may flake and adhere to the food instead of remaining as a continuous film adhering to the sheet material.

When process cheese or other molten foods are packaged in such coated sheet material, the packages are often placed in refrigerators where they are chilled and brought into a humid room so as to produce condensation of moisture on the surface of the package causing the coating film to separate from the sheet material and remain upon the food about which the sheet is wrapped. I! such fllm does not retain its flexibility as well as its self-sustaining characteristics it will be diflicult to remove the film from the food.

h In packaging process cheese, for example, in accordance with the method disclosed in Abrams et a1. Patent No. 2,077,301, the coated sheet is lined in a wooden box and the like with the film or coating iacing'the interior of the container. The molten cheese is thenpoured into contact with the coating, the air is expelled from the package, and the overlapping portions of the wrapper are then hermetically heat-sealed. American process cheese, for example, may be poured into such lined containers at a' temperature of about to F. After the package is completedthe hot cheese will remain in contact with the coating on the sheet or wrapper for a considerable period of time. In fact, it is the practice of cheese manufacturers after packaging the cheese in such wrapper tostore the boxes containing the packaged cheese for about twelve to sixteen hours to permit the cheese to cool. During such time the coating on the sheet is subjected to relatively high temperatures and then to slow cooling. During such time the coating is in softened condition which is desirable in order to cause intimate contact of th coating with the cheese. However, as a result of these severe temperature conditions and slow coolin the coating'material tends to become brittle and loses its flexibility, so that when the package of cheese is opened for use, the sheet material will separate from th coating and leave particles of the composition on the cheese.

It is therefore desirable to modify the composition of wax and rubber as disclosed in the aforementioned patents so that the coating on the sheet will soften suflicientlyto permit intimate contact with the food and yet retain its self-sustaining characteristics in spite of the long exposure to heat as well as the slow cooling.

We have discovered after considerable experimentation that these difilculties can be overcome by adding to the composition a controlled quantity of microcrystalline or amorphous waxes. Any suitable amorphous or microcrystalline waxes may be used for the purpose of our invention. For example, "Barnsdall special wax" sold by the Barnsdall Refinery Company, is satisfactory. Also Cerese" waxes sold by the Soccny Vacuum Company, carnauba, synthetic waxes, hydrogenated vegetabl oils such as hydrogenated cottonseed oil. soya bean oil, and castor oil; also hydrogenated animal oils such as fish oils; also hydrogenated waxes such as I. G. wax, also beeswax, candelilla, spermaceti, and wool wax, are suitable. The term "amorphous wax" is intended to include all these substances.

The following is an illustration of a composition suitable for coating sheet materials for use in packaging molten foods such as American process cheese at, say, 150-155 F.

Per cent by weight Pale crepe rubber 18 Amorphous wax--Barnsdall special wax (165' F. M. P.) 39

Paraflin wax (120-140" F. M. P.) 43

In compounding the composition the waxes are first melted and maintained at a temperature from about 180 to 220 F. The rubber, preferably in the form of pale crepe sheets, is added in small pieces to the molten wax mixture and stirred until the rubber is completely penetrated by the wax. The mixture is then thoroughly stirred in a Werner-Pfieiderer mixer for about 1% to 2 hours while the temperature is maintained at around 180 to 190 F. until a uniform homogeneous composition is obtained. As soon as the mixture is entirely smooth it is coated while hot upon any suitable base sheet by any well known means, such as by means of a, hot roll or doctor bar. The composition is compounded so as to have a minimum viscosity oi 8,000 seconds (50 cc. measured on a Scott viscosimeter at 90 C.). It is important that the viscosity is not lowered below this value during compounding because if this occurs the film produced from the composition will not have the desired self-sustaining characteristics as well as flexibility pliabilityyand the like. It is also important that the temperature during the compounding should not be higher than about 200 F. in order not to scorch or burn the rubber, as this will impart an undesirable color and odor to the composition which will be objectionable when used for packaging food products.

The following is an example of a composition coated on a sheet material suitable for packaging molten foods having a higher melting point than American process cheese, e. g. 160-165 F.:

Per cent by weight Rubber 18 Ester gum- 8 Amorphous wax (165 F. M. P.) 44 Parafiln wax (145 F. M. P.) 30

fin wax or other equivalent crystalline waxy constituent may range anywhere from 94 to percent by weight. According to our invention we combine with the crystalline parafiin wax a controlled proportion of an amorphous or microcrystalline wax anywhere in the range from about 5 to 50 percent by weight of the total paraflln wax used. As previously explained, we have found that the addition of amorphous wax to a composition containing crystalline paraffln wax and rubber, serves to increase the pliability and flexibility of the film after it has been subjected to high temperatures and then cooled slowly over an extended period of time. The film after such treatment also will not crumble or separate from the sheet to which it has been applied.

Our composition may be applied to any suitable sheet material such as Pliofilm, Cellophane (regenerated cellulose), cellulose acetate, ethyl cellulose films, casein sheets, sulphite paper, kraft paper, parchment paper, glassine, metal foil, fabric, rayon, sheets made of synthetic resinous substances, and the like. The composition will not penetrate or saturate the sheet material to which it is applied, but it will remain as a selfsustaining continuous film upon the surface of the sheet and when used for packaging molten or hot foods which are brought in contact with said film, the film will retain its pliability and flexible characteristics so that when the wrapper is peeled from the packaged food the film will adhere to the sheet material and will not becomebrittle. crumble, or fall apart and thereby contaminate the food in the package. Even if the coating film should separate from the base sheet when wet,

the film will retain its strength and elasticity so as to be self-sustaining without crumbling or fall ing apart. When non-wetting sheet materials are used such as Pliofilm. cellulose acetate, foil, and the like, the coating film will not readily separate when the coated sheet is wet.

The invention is not restricted to the use of rubber in the composition and it is to be understood that any suitable film forming material similar to rubber in its characteristics can be used, such as synthetic rubber, Vistanex (isobutylene polymers), gutta percha, balata, smoked sheet rubber, chlorinated rubbers and the like.

It is to be understood that numerous modifications and changes may be made in our coat-.

ing composition, and that it is intended to include such modifications within the scope of the appended claims.

We claim:

1. A coated sheet material suitable for packaging molten food materials such as process cheese and the like which comprises a sheet material having a superficially adherent, self-sustaining, flexible film of tangible thickness formed from a hot melt composition having a viscosity of at least 8,000 seconds (50 cc. measured on a Scott viscosimeter at 90 C.) comprising a uniform homogeneous mixture of 6 to 50% by weight of rubber, 94 to 50% by weight of paraffin wax and an amorphous wax blended with the paramn wax in amount for the film to have flexibility and self-sustaining characteristics after pouring and slow cooling of hot molten materials in direct contact therewith.

2. A coated sheet material suitable for packaging molten food materials such as process cheese and the like which comprises a sheet material having a superficially adherent, selfsustaining, flexible film of tangible thickness formed from a hot-melt composition having a viscosity of at least 8,000 seconds (50 cc. measured on a Scott viscosimeter at 90 C.) comprising a uniform homogeneous mixture of 6 to 50% by weight of rubber, 94 to 50% by weight of paraflin wax and a controlled quantity of an amorphous wax blended with the parafiln wax in amount from to 50% by weight of the paraflin wax, said film having flexibility andself-sustaining characteristics after pouring and slow cooling of hot molten materials in direct contact therewith.

3. A coated sheet'material suitable for packaging molten food materials such as process cheese and the like which comprises a regenerated cellulose sheet material having a superflclally adherent, self-sustaining, flexible fllm of tangible thickness formed from a hot-melt composition having a viscosity of at least 8,000 seconds (50 cc. measured on a Scott viscosimeter at 90 C.) comprising a uniform homogeneous" of tangible thickness formed from a hot-melt composition having a viscosity of at least 8.000 seconds cc. measured on 9. Scott viscosimeter at C.) comprising a uniform homogeneous mixture of 6 to 50% by weight of a wax-compatible film-forming constituent selected from the group consisting of natural and synthetic rubber, gutta percha, balata, chlorinated rubber, and isobutylene polymers, 94 to 50% by weight of paraflin wax and an amorphous wax blende with the para!- fln wax in amount for the fllm- 0 have flexibility and self-sustaining characteristics after pouring and slow cooling 0! hot molten materials in direct contact therewith.

5. A coated sheet material suitable for P801!- aging molten food materials such as process cheese and the like which comprises a sheet material having a superficially adherent, selfsustaining, flexible film of tangible thickness formed from a hot-melt composition having a viscosity of at least 8,000 seconds (50 cc. measured on a Scott 'viscosimeter at 90 C.) comprising a uniform homogeneous mixture of 6 to 50% by weight of rubber, 94 to 50% by weight 0! paraflin wax and a microcrystalline wax blended with the paramn wax in amount for the film to have flexibility and self-sustaining characteristics after pouring and slow cooling of hot molten materials in direct contact therewith.

ALLEN ABRAMS. GEORGE W. FDRCEY. CHARLEY L. WAGNER. 

